Wimax: Features And Applications

Transcript

WiMAX: Features and Applications Mihai-Ionuţ ANDRIEŞ*, Ion BOGDAN*, Ştefan-Victor NICOLAESCU**, Luminiţa SCRIPCARIU* Cuvinte cheie. WiMAX, Mobile WiMAX, comparaţii Key words. WiMAX, Mobile WiMAX, comparisons WiMAX/WiFi WiMAX/WiFi Rezumat. Lucrarea prezintă principalii parametri ai Abstract. The main technical parameters of the WiMAX tehnologiei WiMAX şi apreciază rolul ei în ansamblul technology are presented and its role in the modern tehnologiilor moderne de comunicaţii. Sunt realizate communication technologies is envisaged. Comparisons comparaţii cu tehnologia WiFi şi se subliniază with WiFi technology are made and the main principalele advantages of its variant for mobile com-munications avantaje ale variantei pentru comunicatâţii mobile (Mobile WiMAX). În final sunt (Mobile discutate posibilele evoluţii ale standardului. development of the standard are discussed. 1. Introduction* meeting was held (February 1980). The services WiMAX (Worldwide Interoperability for Microwave Access) is a relatively new standard based on the IEEE 802.16 family of Wireless MAN (Metropolitan Access Networks) standards [1], [2], [3]. It is datacentric and aimed at fixed and mobile applications. It fills the gap between low mobility data-centric standards such as IEEE 802.11 (WLAN - Wireless Local Area Network) and high mobility voice-centric standards such as GSM. Other standards fit within this category such as 3G and their future versions, but the market in this area is big, enabling several players to co-exist. IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks. More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. The number 802 was simply the next free number IEEE could assign, though “802” is sometimes associated with the date the first * ** “Gheorghe Asachi” Technical University of Iassy. National Institute for Studies and Researches in Com- munications (INSCC), Bucharest. TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX) are underlined. Finally, future and protocols specified in IEEE 802 map to the lowest two layers (Data Link and Physical) of the seven-layer OSI networking reference model. IEEE 802 splits the OSI Data Link Layer into two sublayers denoted as Logical Link Control (LLC) and Media Access Control (MAC), respectively. WiMAX describes the interoperable implementations of IEEE 802.16 wireless networks [4], [5], [6]. It promises to solve the distance limitations of Wi-Fi (802.11) by offering 70 Mbps speeds station - a sufficient amount of bandwidth to simultaneously support hundreds of businesses with T1/E1-type connectivity and thousands of homes with DSL-type connectivity - with a single base station over a 50 Kilometers of service area, allowing users to get broadband connectivity without the need of direct line-of-sight (LOS) to the base station. It provides interoperable broadband wireless connectivity to fixed, portable and nomadic users. The technology also promises to enable operators to rollout the network at significantly lower costs than wired broadband or 3G. So WiMAX is a highcapacity, open standard, IP-based technology that 7 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu can be deployed as a new network installation or as HiperMAN and WiMAX selected the common an overlay to complement existing 2G or/and 3G mode of operation of these two standards, that is wireless networks. In either case WiMAX networks 256FFT OFDM. Concentrated in 2-11 GHz Wireless are capable of interworking with cellular and wired MAN, it has the following set of features: networks. High speed Internet access, services and • Service area range 50 Km; applications supported by WiMAX can deliver higher • NLOS operation; revenues per user, new subscribers, lower churn, • QoS (Quality of Service) designed in for and additional revenues from wholesale and new voice/video, differentiated services; • Very high spectrum utilization: 3.8 bit/Hz; service partners. • Up to 280 Mbps per base station; The massive range and the high speeds claimed by the WiMAX proponents do not reflect, however, the • True broadband for portable users - based on actual performance that can be experienced by users IEEE 802.16e connectivity for laptops and PDAs in field deployments [7], [8]. The often-mentioned 70 (Personal Digital Assistant) with integrated WiMAX Mbps speed on a WiMAX network is the total shared technology. bandwidth capacity available to multiple users on a 2 x WiBro [11] is the service name for Mobile 20 MHz frequency spectrum. Actually, per user data WiMAX in Korea and uses the same standards, rates are likely to be around 1–3 Mbps only. The promised 50 Km range can be reached only in LOS deployments, which are not possible in most areas due to obstructions presented by buildings and trees. Practical deployments indicate that coverage of 1–3 Km in urban areas and 5–10 Km in rural areas are more realistic limits [9], [10]. Expectations of rolling out system and certification profiles and certification processes as Mobile WiMAX. It has the same functionality defined by the Mobile WiMAX system profile, with identical PHY, MAC and Power Classes, uses equipment to be certified under one of the Mobile WiMAX certification profiles that designate frequency, duplexing and bandwidth requirements. The Koreans sought to develop WiBro as a regional WiMAX networks, using a few radio towers to cover a and potentially international alternative to 3.5G or large city and offering DSL-type speeds are not 4G feasible yet. momentum as a standard, WiBro has joined WiMAX cellular systems. But given the lack of WiMAX seeks to build on the success of and agreed to harmonize with the similar OFDMA established business models that have reaped 802.16e version of the standard. WiBro will go up benefits in the field. WiMAX represents a significant against 3G and very high bandwidth wire-line leap forward in ensuring the standardization of the services rather than as gap-filler or rural under- Wireless MAN protocols. OFDM and NLOS (non- served market deployments as is often exampled as LOS) technology can be used to backhaul 802.11 the 'best fit' markets for WiMAX. hotspots and WLANs to the Internet, provide campus connectivity, and enable a wireless alternative to cable and DSL for last mile broadband access. 2. Spectrum allocation issues The 802.16 specification applies across a wide Similar to IEEE 802.16 is the European (ETSI) swath of the RF spectrum. However, there is no standard HiperMAN. WiMAX and HiperMAN are uniform global licensed spectrum for WiMAX (Table 1 partially based on same IEEE standards. and Table 2). Each geographical region defines and 8 TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX: Features and Application regulates its own set of licensed and license-exempt (AWS). There are several variants of 802.16, bands. In the US, the biggest segment available is depending on local regulatory conditions and thus on around 2.5 GHz and it is already assigned. which spectrum is used, even if everything but the Elsewhere in the world, the most bands used are underlying radio frequencies is the same. WiMAX around 3.5 GHz, 2.3/2.5 GHz or 5 GHz, with 2.3/2.5 equipment is not, therefore, as portable as it might GHz being most important in Asia. In addition, several have been - perhaps even less so than Wi-Fi, whose companies have announced plans to utilize the WiMAX assigned channels in unlicensed spectrum vary little standard in the 1.7/2.1 GHz spectrum band for the from jurisdiction to jurisdiction. The actual radio deployment in USA of "Advanced Wireless Services" bandwidth of spectrum allocations is also likely to vary. Table 1 WiMAX band allocation around the World Country/Geographic area Bands Used North America , Mexico 2.5GHz and 5.8GHz Central and South America 2.5GHz , 3.5GHz and 5.8GHz Western and Eastern Europe 3.5GHz and 5.8GHz Middle East and Africa 3.5GHz and 5.8GHz Asian Pacific 3.5GHz and 5.8GHz Table 2 Frequency bands’ availability for WiMAX Band Frequencies License required 2.5 GHz 2.5 to 2.69 GHz Yes 3.5 GHz 3.3 to 3.8 GHz but primarily 3.4 to 3.6 GHz Yes , in some countries 5 GHz 5.25 to 5.85 GHz No Availability Allocated in Brazil, Mexico, some Southeast Asian countries and the U.S. (The WiMAX Forum also includes 2.3 GHz in this band category because it expects to cover 2.3 GHz with the 2.5 GHz radio.) In most countries the 3.4 GHz to 3.6 GHz band is allocated for broadband wireless In the 5.725 GHz to 5.85 GHz portion many countries allow higher power output (4 watts) which can improve coverage Because WiMAX’s goal is to promote the The frequency band between 10 and 66 GHz is interoperability of equipment based on either the provided for LOS solutions for a variety of licensed 802.16d or HiperMAN standards, the WiMAX Forum frequencies (10.5, 25, 26, 31, 38 and 39 GHz) and the 2 has chosen to support the 256 OFDM mode to 11 GHz frequency band for NLOS solutions over both exclusively and to only certify equipment supporting licensed and license-exempt frequencies. The minimum that particular PHY mode. Wi-Fi 802.11a and channel bandwidth for WiMAX is 1.75 MHz per channel, 802.11g also use OFDM and have established an 10 MHz being considered as an optimum. It remains to excellent performance record for robust wireless be seen what impact potential interference may have, networking. However, Wi-Fi uses 64 OFDM. especially on QoS commitments. TELECOMUNICAŢII ● Anul L, nr. 1/2007 9 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu WiMAX equipment operating in license-exempt frequency bands uses time-division duplexing (TDD) and equipment operating in licensed frequency bands uses either TDD or frequency-division duplexing (FDD). WiMAX supports a variety of wireless broadband connections: • High-bandwidth MANs to home and smallbusiness users, replacing DSL and cable modems; • Backhaul networks for cellular base stations, 3. The 802.16 standards and deployment bypassing the public switched telephone network. evolution WiMAX’s channel sizes range from 1.25 MHz to WiMAX has two versions: one based on the IEEE 802.16 standard for fixed networks and another on the IEEE 802.16e standard for mobile networks, which is the latest. This version also supports a form of multiple-input-multiple-output (MIMO), so more than one receiver might be needed in the mobile device. IEEE 802.16 was originally design to be a radio standard for cost-effective last-mile broadband connectivity to users not served by wired broadband 20 MHz, giving a WiMAX network the flexibility to support a variety of data rates such as T1 (1.5Mbps) and higher. This flexibility allows WiMAX to adapt to the available spectrum and channel widths in different countries or licensed to different service providers. Equally important, quality-of-service features ensure high performance for voice and video. WiMAX employs 64-state quadrature amplitude modulation (64QAM) and orthogonal frequency- such as DSL or cable. By now, this WMAN (Wireless division multiplexing (OFDM), which together demand MAN) standard is addressing a broader market for exceptionally high linearity so the subcarrier spacing mobile, low-cost, high-speed broadband connections. It ( Δf ) is set to 10 KHz. WiMAX systems also require is optimized for high, bursty data-rates, but can good error-vector-magnitude (EVM) performance as a simultaneously support real-time multimedia and benchmark of modulation fidelity. isochronous applications such as Voice-over-IP (VoIP). For fixed wireless and mobile NLOS applications The current 802.16 standard is IEEE 802.16e- OFDMA can be used. SOFDMA (Scalable OFDMA) 2005, approved in December 2005. It followed on improves upon OFDM256 for NLOS applications. from IEEE 802.16-2004 (known as "fixed" or This can be made utilizing advanced antenna "nomadic" WiMAX), which replaced IEEE Standards diversity schemes, and hARQ (hybrid-Automatic 802.16-2001 (the original WiMAX standard for the Retransmission Request). Using high-performance 10 to 66 GHz), 802.16c-2002, and 802.16a-2003. coding techniques such as Turbo Coding and Low- IEEE 802.16d) Density Parity Check (LDPC) will enhance security addresses only fixed systems. 802.16e adds mobility and NLOS performance. Using downlink sub- components to the standard. channelization, 802.16-2004 (also known as IEEE 802.16e-2005 (known as 802.16e or Mobile WiMAX) an improvement on administrators to trade coverage for capacity or vice versa. For improved the coverage there were introduced Adaptive Antenna modulation schemes stipulated in the original (fixed) Systems and MIMO technologies that eliminate WiMAX standard. The WiMAX standard enables channel bandwidth dependencies on sub-carrier system vendors to create many different types of spacing and allow for equal performance under any WiMAX-based products, including various configu- RF channel spacing (1.25-20 MHz). This brings rations of base stations and customer premise potential benefits in terms of coverage, self installation, equipment (CPE). power consumption, frequency re-use and bandwidth 10 provides allow TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX: Features and Application efficiency. Enhanced Fast Fourier transform (FFT) the 802.11 standard. As previously stated, the larger algorithm can tolerate larger delay spreads, increasing number of subcarriers over the same band results in resistance to multipath interference [12]. narrower subcarriers, which is equivalent to larger In the case of 802.16d and 802.16e standards symbol periods. The same percentage of guard time or the lower frequencies suffer less from inherent cyclic prefix (CP) provides larger absolute values in signal attenuation and therefore give improved time for larger delay spread and multi-path immunity. The minimum received signal in the downlink range and in-building penetration. Systems based on the IEEE 802.16-2004 standard are the only standardized OFDM based Wireless MAN platforms. In the case of 802.16-2004, the OFDM signal is divided into 256 carriers instead of 64 as with direction is 91 dBm. The standard specifies the maximum adjacent channel rejection to be 11 dB. The specifications for IEEE802.11a and IEEE802.16e receivers are shown in Table 3. Table 3 IEEE Design Specifications for WiFi and WiMAX Modulation Coding Rate QPSK 16-QAM 64-QAM SNR (dB) Input Sensitivity (dBm) Data Rate (Mbps) 5 –80 12 7 8 –78 18 WiFi WiMAX 1/2 5 3/4 1/2 10 10,5 –73 24 3/4 14 14 –71 36 1/2 18 18 3/4 19 20 The standard improves in several key aspects, –66 48 –65 54 eases the effect of multipath, allowing for wide but mainly in multi-path interference, delay spread, channels, and robustness. bandwidth. This gives IEEE 802.16 the ability to Multi-path interference and delay spread improve performance in situations where there is not a direct line-of-sight path between the base station and the typically greater than 10 MHz in provide very high capacity links on both the uplink and the downlink. The original IEEE 802.16 MAC was enhanced to is accommodate different PHYs and services, which optimized for long-distance links because it is address the needs of different environments. The designed to tolerate longer delays and delay standard is designed to accommodate either Time variations. The 802.16 specification accommodates Division Duplexing (TDD) or Frequency Division MAC management messages that allow the base Duplexing (FDD) deployments, allowing for both full station to query the subscriber station, but there is a and half-duplex terminals in the FDD case. subscriber station. The 802.16-2004 MAC certain amount of time delay. The standard covers both the MAC and the PHY (PHysical laYer). A 4. MAC number of PHY considerations were taken into The MAC was designed specifically for the PMP account for the target environment. At higher (Point-to-MultiPoint) wireless access environment. It frequencies, line of sight is a must. This requirement supports higher layer or transport protocols such as TELECOMUNICAŢII ● Anul L, nr. 1/2007 11 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu ATM (Asynchronous Transfer Mode), Ethernet or IP systems with overlapping functionality such as (Internet Protocol), and is designed to easily UMTS and cdma2000, as well as a number of accommodate future protocols that have not yet Internet oriented systems such as HiperMAN and been developed. The MAC is designed for very high WiBro [13]. bit rates (up to 268 Mbps each way) of the truly Two of the three major 3G systems, cdma2000 broadband PHY, while delivering ATM compatible and UMTS, compete with WiMAX. Both offer DSL- QoS; the frame structure allows terminals to be class Internet access in addition to phone service. dynamically assigned uplink and downlink burst UMTS has also been enhanced to compete directly profiles according to their link conditions. This allows a with WiMAX in the form of UMTS-TDD, which can trade-off between capacity and robustness in real-time, use WiMAX oriented spectrum and provides a more and provides roughly a two times increase in capacity consistent, if lower bandwidth at peak, user on average when compared to non-adaptive systems, experience than WiMAX. 3G cellular phone systems while maintaining appropriate link availability. usually benefit from already having entrenched The 802.16 MAC uses a variable length PDU infrastructure, being upgrades from earlier systems. (Protocol Data Unit) along with a number of other Users can usually fall back to older systems when concepts that greatly increase the efficiency of the they move out of range of upgraded equipment, standard. Multiple MAC PDUs may be concatenated often relatively seamlessly. The major cellular into a single burst to save PHY overhead. Additionally, standards are being evolved to so-called 4G, high multiple SDU (Service Data Unit) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent across frame boundaries to guarantee the QoS of competing services. And payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers. The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups, can steal bandwidth already allocated to make requests for more, can signal the need to be polled, and they can piggyback requests for bandwidth. the marketplace, 4G is the 3GPP Long Term Evolution effort. For AMPS/TIA derived standards such as cdma2000, a replacement called Ultra Mobile Broadband is under development. In both cases, existing air interfaces are being discarded, in favor of OFDMA for the downlink and a variety of OFDM based solutions for the uplink. These will bring Internet access speeds comparable to, or better than, WiMAX. 6. 802.16 (WiMAX) vs. 802.11 (WiFi) Possibly due to the fact that both WiMAX and WiFi begin with the same two letters, and are based upon IEEE standards no. 802.xx, and are vaguely to do wireless connectivity and the Internet, confusions having in common the use of OFDM, the use of multiple pilot tones, and the support of modulations WiMAX's main competition comes from widely deployed wireless 12 services built on top. With GSM/UMTS, the move to between the two are frequent [14], [15], [16]. Despite 5. Competing technologies Within bandwidth, low latency, all-IP networks with voice ranging from BPSK to 64 QAM, they have some major differences, as follows: TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX: Features and Application 1. Rather than a fixed 20 MHz bandwidth with 52 challenge to the system design is that the subcarriers as in 802.11, WiMAX systems can use subcarriers are spaced more closely together, so variable bandwidths from 1 to 28 MHz with 256 there are tighter requirements for phase noise and subcarriers (192 data subcarriers) in either licensed timing jitter. This translates to a need for higher- or unlicensed spectrum. performance synthesizers. 2. WiMAX supports subchannelization, meaning 4. WiMAX uses a variable-length guard interval that instead of transmitting on all 192 data subcarriers, to improve performance in multi-path environments. one can transmit on just a subset. Using the same The guard interval is a time delay at the beginning of amount of power over fewer carriers, the system the achieves greater range. Because CPE is typically interference. With a very clear channel, the guard limited in power, concentrating the power over fewer interval can be shortened, increasing the throughput. subcarriers in the uplink can balance the power in the With more subcarriers, and with a variable-length uplink and downlink, and enable greater range. guard interval, a WiMAX system's overall spectral 3. The larger number of subcarriers gives WiMAX an advantage over 802.11; the resulting packet to compensate for multi-path efficiency will be 15 to 40% higher than a WiFi system (Table 4). Table 4 Wireless Standards’ Spectrum Efficiency Channel Bandwidth Maximum Data Rate Maximum Efficiency 802.16a 10, 20 MHz; 3.5, 7, 14 MHz; 3, 6 MHz 70 Mb/s 5 bps/Hz 802.11a 20 MHz 54 Mb/s 2.7 bps/Hz EDGE 200 KHz 384 Kbps 1.9 bps/Hz cdma2000 1.25 MHz 2 Mb/s 1.6 bps/Hz 5. Error-vector magnitude (EVM) requirements Tx/Rx requires two complete radios. However, FDD for 802.11 are specified at -25 dB, which is required will allow greater throughput, as bandwidth is to achieve a 10% packet error rate. For 802.16, dedicated for receive and transmit, and this EVM is held to -31 dB, which is based on a 1% bandwidth is used simultaneously. The 802.11 packet error rate. This lower error rate helps standard provides one-fourth of the OFDM options contribute Also for CP than does the 802.16-2004 standard, which contributing to the longer range is the receiver noise provides 1/32, 1/16, 1/8 and 1/4, where each can be figure, optimally set. to which WiMAX’s is more longer stringent range. for 802.16. Specifically, 802.11's maximum noise figure is 10 dB, while 802.16 operates at 7 dB. 7. Another significant difference between WiMAX and 802.11 is ranging and dynamic transmit range. 6. WiFi only supports time division duplexing In 802.11, the output power is virtually fixed, and (TDD). In contrast, the 802.16 specifications offer systems typically transmit at the same power all the more flexibility, supporting TDD, FDD, and H-FDD. time. However, for WiMAX, a ranging process An FDD system will cost more because simultaneous determines the correct timing offset and power TELECOMUNICAŢII ● Anul L, nr. 1/2007 13 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu settings. This process ensures that transmissions 10. WiMAX is more secure than Wi-Fi: WiMAX from each subscriber station arrive at the base will actually use a similar authentication and encryption station at the proper time and at the same power scheme to the Wi-Fi WPA2 standard. The minor level. As a result, the 802.16 standard requires that difference is that WiMAX security will use either 3DES subscriber stations have a 50-dB dynamic transmit or AES encryption and a flavor of Extensible range. This allows systems that are close to the base Authentication Protocol (EAP) called PKM-EAP. Wi-Fi station to back off their transmit power, while those far WPA2 on the other hand will typically use PEAP away can transmit at maximum power. This is authentication along with AES encryption. significant because WiMAX supports transmit ranges of several Kilometers, and transmitting at maximum power near the base station would be disastrous. 11. WiMAX is very different from Wi-Fi in the way it works - MAC layer/ Data Link Layer. • In Wi-Fi the MAC uses contention access - all 8. WiMAX is longer in range than Wi-Fi: WiMAX subscriber stations that wish to pass data through a is a long range - many Kilometers system, which wireless access point (AP) are competing for the uses licensed spectrum to deliver a point-to-point AP's attention on a random interrupt basis. This can connection to the Internet from an ISP to an end cause subscriber stations distant from the AP to be user. WiMAX furnishes broadband connectivity over repeatedly interrupted by closer stations, greatly a much wider area than Wi-Fi and does not require a reducing their throughput. This makes services such direct line of sight between subscriber terminals and as VoIP or IPTV, which depend on an essentially access points. This distinction points up the constant difference between the two standards: Wi-Fi is a LAN interruptibility, difficult to maintain for more than a technology, while WiMAX is a MAN technology. The few simultaneous users. QoS depending on data rate and “metropolitan” in “MAN” does not restrict WiMAX to • In contrast, the 802.16 MAC uses a scheduling urban environments, however. This technology is ideal algorithm for which the subscriber station need for providing broadband services in rural areas that compete once (for initial entry into the network). may be underserved by DSL or cable. After that it is allocated an access slot by the base 9. Different 802.16 standards provide different types of access, from mobile (analogous to access via a cellphone) to fixed (an alternative to wired access, where the end user's wireless termination point is fixed in location). WiMAX is designed to operate in both the licensed radio band and unlicensed radio band. When WiMAX operates in the licensed radio band, it is free to broadcast with station. The time slot can enlarge and contract, but remains assigned to the subscriber station which means that other subscribers cannot use it. The 802.16 scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control QoS parameters by balancing the time-slot assignments among the application needs of the many times more channels and power that any subscriber stations. WiMAX also addresses the unlicensed radio solution, as long as the broadcaster requirements of those subscribers that want to be owns the license for that radio band. This means able to use their broadband connection regardless of that licensed WiMAX operation will typically be used location, functionality that DSL and cable modem by Wireless ISP operators. services do not support. 14 TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX: Features and Application to-net, flexible channel bandwidth is imperative for 7. Main advantages of Mobile WiMAX cell planning. The 802.16-2004 standards have a) Advanced IP-based architecture strong commercial backing to go along with its WiMAX is a next-generation technology that will technical capabilities. facilitate the cellular operators’ transition to all-IP networks. Cellular networks are also moving towards c) QoS robust control an IP core with the LTE and System Architecture Several features of the WiMAX protocol ensure Evolution (SAE) efforts. WiMAX fully supports IMS2 robust and its 3GPP2 counterpart, Multimedia Domain services such as streaming audio and video. As with (MMD), emerging architectures that will enable any other type of network, users have to share the service providers to introduce a wide range of rich data capacity of a WiMAX network, but WiMAX’s voice and data applications rapidly and at a low QoS features allow service providers to manage the marginal cost. With IMS and MMD, service providers traffic can develop applications independently of the agreements access layered providers can therefore charge a premium for architecture in which application modules can be guaranteed audio/video QoS, beyond the average easily modified or reused. The IP core network at data rate of a subscriber’s link. the basis of WiMAX will simplify interworking with WiMAX other IP technologies. Support for IMS and MMD will mechanism for letting users into the network. This further facilitate interworking and remove existing mechanism’s operation and value become apparent redundancies in the core network. At the beginning, from a comparison of WiMAX with the CSMA/CD or however, WiMAX will have to be seamlessly CSMA/CA mechanisms used in LAN technologies integrated with existing cellular networks [17], [18]. such as 802.11. When a CSMA/CA-based wireless technology within a flexible quality-of-service based on on QoS a (QoS) each subscriber’s link-by-link provisioning protection is basis. for service Service One aspect of a grant-request LAN has fewer than 10 users per access point, the b) Flexible channel bandwidth network experiences little contention for use of As the distance between a subscriber and the airtime. Occasional packet collisions occur, and they base station (or AP) increases, or as the subscriber require back-off and retransmissions, but the starts to move by walking or driving in a car, it resulting overhead does not waste a significant becomes more of a challenge for that subscriber to amount of bandwidth. transmit successfully back to the base station at a If the number of CSMA/CA access-point users given power level. The IEEE 802.16-2004 and IEEE goes up to dozens or hundreds of users, many more 802.16e standards have flexible channel bandwidths users tend to collide, back-off and retransmit data. In between 1.5 and 20 MHz to facilitate transmission such an environment, average network loading over longer ranges and to different types of factors can easily raise past 20 to 30 percent and subscriber platforms. In addition, this flexibility of users notice delays—especially in streaming-media channel bandwidth is also crucial for cell planning, services. WiMAX avoids such issues by using a especially a grant-request mechanism that allocates a small dedicated antenna, each sector has the potential to portion of each transmitted frame as a contention reach users with more throughputs over longer slot. With this contention slot, a subscriber station ranges than can an omni-directional antenna. Net- can enter the network by asking the base station to in the licensed spectrum. With TELECOMUNICAŢII ● Anul L, nr. 1/2007 15 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu allocate an uplink (UL) slot. The base station addition to these general-purpose QoS features, evaluates the subscriber station’s request in the WiMAX provides specific QoS support for voice and context of the subscriber’s service-level agreement video. To enable toll-quality voice traffic, for and allocates a slot in which the subscriber station example, voice packets can be tagged as such. The can transmit (send UL packets). The WiMAX grant- base-station’s scheduler then manages the passage request mechanism establishes a fixed overhead for of these packets through the air interface to provide airtime contentions and prevents large numbers of deterministic latency. subscribers from interfering with one another. Overall, the mechanism allows for much higher utilization of d) Superior performance available channel resources. Even when a base station WiMAX meets all the requirements for mobile has thousands of users and a high load factor, the Internet network does not bog down with packet collisions and mechanisms, ranging from hard handoffs (with retransmissions. As more users join a WiMAX network, break-before-make links) to soft handoffs (with the base station schedules the subscribers using make-before-break dynamic scheduling algorithms that the service mechanisms for mobile devices, advanced QoS and provider can define and modify to achieve the low latency for improved support of real-time promised level of service to each subscriber. applications, Another aspect of WiMAX QoS provisioning is access. It supports and links), advanced multiple handoff power-saving Authorization, Authentication, and Accounting (AAA) functionality. link-by-link data-rate manageability. The signal The advanced performance of mobile WiMAX is strength between base and subscriber stations largely tied to its use of OFDMA, a multiplexing affects a wireless link’s data rate and ability to use technique well suited to multipath environments that various modulation schemes within the 256 OFDM gives network operators higher throughput and frameworks. Signal strength depends mainly on the capacity, great flexibility in managing spectrum distance between the two stations. If the network resources, and improved indoor were restricted to a single modulation scheme per WiMAX performance is further enhanced by the carrier, subscribers that are farther away from the base use of Time Division Duplex (TDD), but it can also station would limit the network’s ability to use the most efficient scheme. WiMAX enables optimization of each subscriber’s data rate by allowing the base station to set modulation schemes on a link-by-link basis. A subscriber station close to the base station could use 64QAM modulation, while the weaker signal from a more remote subscriber might only permit the use of support Frequency Division Duplex (FDD) which dominates in 3G networks. Whereas FDD keeps the uplink and the downlink channels separate in frequency, TDD is a less complex, more efficient mechanism that uses a single frequency channel, with uplink and downlink traffic separated by a guard time. In addition, for IP-based services the use of a single channel for the uplink and the downlink 16QAM or QPSK. The 802.16 MAC can even use a makes it substantially less complex and more cost- different modulation method for each subscriber’s effective to implement MIMO and beamforming in downlink and uplink bursts. WiMAX networks than in CDMA-based networks. Optimizing and MIMO and beamforming are expected to bring a maximizing each subscriber’s data rate establishes substantial improvement in throughput in TDD- a solid foundation for high quality of service. In based WiMAX networks. 16 overall bandwidth usage TELECOMUNICAŢII ● Anul L, nr. 1/2007 WiMAX: Features and Application e) Flexibility MHz to 10 MHz. This gives operators the flexibility to WiMAX was designed from the ground up to be use WiMAX in multiple spectrum bands and with the an all-IP technology that is optimized for high- amount of spectrum they have. WiMAX Forum throughput, real-time data applications and that is Certified equipment will be approved in additional not beholden to a legacy infrastructure. WiMAX can spectrum bands in response to the needs of be deployed both in deployments, where network operators operators rely exclusively on WiMAX for the edge recognizes the importance of spectrum availability to infrastructure, and in overlay or complementary network operators and is taking a proactive role in networks, where operators embed WiMAX within their promoting an increased availability of spectrum for networks to increase capacity and throughput as WiMAX deployments. necessary to deliver true wireless broadband service. high capacity and high-throughput broadband services. Mobile WiMAX broadband networks offer service providers a profitable model to deploy multiple value-added services that bring in additional revenues streams. The additional cost of bundling new mobile services with existing ones is low, as the operators already have an established relationship with the subscriber and can leverage their existing marketing, branding and customer service operations to support the new services. Global roaming among WiMAX service providers will allow subscribers to access different networks using the same device and a single, familiar interface. Global roaming will become an essential feature of the mobile service offering that will increase the attractiveness to the subscribers and generate additional revenues. If they offer access through their partners using roaming agreements similar to those in place for cellular networks, service providers will be able to get the desired footprint in their market without having to build an extensive infrastructure. Mobile WiMAX can be deployed in several WiMAX Forum WiMAX meets the growing mass-market demand WCDMA and EV-DO use spectrum resources that effective The f) Cost effectiveness Cellular networks based on GSM, CDMA, are limited and typically too expensive for cost worldwide. for cost-effective, high-throughput broadband wireless services. The business case for WiMAX is attractive as the cost of the equipment is kept low by a combination of interoperable components based on open standards, mass adoption of subscriber units, an attractive IPR structure, and a high base station capacity. In turn, its contained infrastructure costs and efficient spectrum utilization allow service providers to address demand from the mass market, by offering personal broadband services at a price point that both business and consumer users will find attractive. Interoperability brings more choices to network operators and increases competition among vendors. Network operators are not dependent on a single vendor to provide both base stations and subscriber units, or to decide the pace and availability of upgrades. The cost of open-standards equipment tends to decrease rapidly with the increase in volume and the market entry of high-volume, low-cost, vendors. Also is possible to make the integration of WiFi and WiMAX in a single chipset. 8. Cost & CPE availability licensed bands (2.3 GHz, 2.5 GHz, 3.3 GHz, and WiMAX backers often talk about inexpensive 3.4-3.8 GHz) with channel sizes ranging from 3.5 customer premise equipment (CPE) and, eventually, TELECOMUNICAŢII ● Anul L, nr. 1/2007 17 Mihai-Ionuţ Andrieş, Ion Bogdan, Ştefan-Victor Nicolaescu, Luminita Scripcariu embedding WiMAX chips in laptops and mobile broadband or 4G and so far iBurst is the only pre- devices. However, delivery of this promise is still in selected solution with over a dozen commercial its infancy. Even when available, early versions are deployments worldwide. IEEE 802.20 was established likely to remain expensive until economies of scale by IEEE as MBWA for operation from 120 to 350 are realized. WiMAX is still at the hype stage and Kmph. The PAR was not for a broad mobile operators need to tread carefully before investing in application. Since conception, the standard has been a big way into setting up networks. re-purposed as filling general requirements for NGMN. The WiMAX certification allows vendors with In so doing, 802.20 standard has taken on many of the 802.16d products to sell their equipment as WiMAX methods certified, thus ensuring a level of interoperability with modulation up to 64 QAM and similar scalable OFDMA other certified products, as long as they fit the same capabilities. It apparently retains fast hand-off, FEC profile. and cell edge enhancements. But 802.20 is being Among the mobile devices that have or are of mobile WiMAX, including dynamic shunned by ETSI 3GPP LTE, major network operators in North America and EU, and is unlikely to become expected to have a WiMAX interface are: • Data centric devices: notebooks, PDAs, Ultra broadly accepted. Compared to mobile WiMAX, the momentum has stalled. Mainstream of development Mobile PCs • CE devices: game consoles, MP3 players efforts for both WiMAX and LTE have shifted to MIMO- • Voice and voice/data devices: cellular phones, AAS-OFDMA and SC-OFDM for LTE on the up-link. WiMAX 802.16e-2005 has been proposed as IP- smartphones • Vertical applications devices: CCTV cameras, OFDMA for inclusion as the sixth wireless link system under IMT-2000. Both WiMAX and LTE will achieve in-vehicle devices. Equipment built to 802.16e is not compatible with 100 Mbps mobile and 1 Gbps fixed-nomadic 802.16d: the 802.16d WiMAX specifications cover only bandwidth goals set by ITU for 4G NGMN systems fixed point-to-point links, while 802.16e addresses both through the adaptive use of MIMO-AAS and smart, fixed and mobile links. The basic appeals of WiMAX granular network topologies. are performance and cost; it costs less than competing cell technologies because it requires far fewer network Acknowledgements elements, they are built in to the basic WiMAX device This paper is partly supported by the Romanian and the shoe box-sized antennas can be mounted to Ministry of Education, Research, and Youth, CEEX grants existing poles or buildings. no. 19/2006 and 172/2006 and it is partly based on the Revision 802.16f is intended to improve multi-hop functionality, and 802.16g is supposed to deal with efficient handover and improved QoS. work done by the first author at LCIS-INP Grenoble, ESISAR, Valence, France. References 1. 9. Future developments: IEEE 802.20 Wireless Access Systems - IEEE Std 802.16.2™-2004 (Revision of IEEE Std 802.16.2-2001) 802.16™, MBWA (Mobile Broadband Wireless Access) is a technology developed by IEEE 802.20. 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Deploying WiMAX Solutions, www.intel.com/netcomms/ /technologies/wimax/306013.pdf TELECOMUNICAŢII ● Anul L, nr. 1/2007 Conference, 13-17 March 2005, vol. 3, pp 1446- 1452 18. R. B. Marks, Evolution of IEEE Standard 802.16 as the Basis of Global Broadband Wireless Access, Pacific Telecommunications Conference, Jan. 1619,.2005, Honolulu, Hawai. 19